1. Field of the Invention
The present invention relates to a moving apparatus utilizing a cam groove.
2. Description of the Related Art
A semiconductor exposure apparatus transfers a pattern of a reticle using a laser beam. Currently, the semiconductor exposure apparatus transfers a pattern having a line width of the order of nanometers. This type of semiconductor exposure apparatus includes an illumination optical system (optical apparatus) to irradiate reticle with light guided from a light source. This illumination optical system includes a plurality of optical components which are used to set a desired illumination condition such as an illuminating region, illuminance, the distribution of illuminance, the shape of an effective light source of a light beam irradiated to a reticle. In the illumination optical system, in order to change the size of, for example, the effective light source, a moving apparatus for moving an optical component is used. As one of such moving apparatuses, a cylindrical cam barrel having a cam groove is used.
FIG. 7 is a perspective view illustrating a cam barrel 61 that includes a conventional cam groove and FIG. 8 is its side view. FIG. 9 is a cross sectional view taken along line 9-9 in FIG. 8. Three cam grooves 62 are formed on the cam barrel 61. These cam grooves 62 are formed in a perpendicular direction, that is, these cam grooves 62 are obliquely formed against a vertical direction in FIG. 8. Inside the cam barrel 61, a moving member 63 is disposed. Three support shafts 64 are fixed on the moving member 63. A bearing 65 such as a rolling bearing is fixed on the support shaft 64. The moving member 63 is supported by the cam barrel 61 via the bearing 65. While the cam barrel 61 and the moving member 63 are relatively rotated, the moving member 63 is moved in a perpendicular direction.
In a conventional cam barrel 61 as described in FIGS. 7 to 9, the support shaft 64 is disposed so that the extended line of the support shaft 64 passes through the rotation center axis O of the cam barrel 61.
However, in such a disposition, in a contact point B where the bearing 65 and the cam barrel 61 come into contact, the bearing 65 and the cam barrel 61 move in a different direction. This accelerates abrasion of the bearing 65 and the cam barrel 61.
FIG. 10 is an enlarged sectional view illustrating a contact portion. The bearing 65 is brought into contact with the cam barrel 61 at the contact point B in the lower surface of the cam groove 62 by the force (gravity) applied to the moving member 63. When the moving member 63 and the cam barrel 61 are relatively rotated, at the contact point B, the cam barrel 61 is moved in a tangential direction D of a circle center on the rotation center axis O. In contrast, the bearing 65 is fixed on the support shaft 64. At the contact point B, the bearing 65 is moved in a direction C perpendicular to the support shaft 64.
If the moving member 63 is moved in the state where a large difference exists in moving directions of the cam barrel 61 and the bearing 65 as described above, the bearing 65 is dragged in the cam groove 62. Thus, abrasion of the bearing 65 and the cam barrel 61 is accelerated. As a result, durability of an apparatus is reduced and an abraded powder is increasingly generated, both of which are not preferable. In particular, weight of an optical component of an exposure apparatus that forms the pattern of a reticle on a wafer tends to increase along with increase in numerical aperture. If the weight of the optical component is increased, the diameter of a bearing which supports the component must be increased to maintain durability. However, if the diameter of the bearing is large, a difference in a moving direction as described above is increased.